Haloaryl carbaboranes: 2. Synthesis and characterisation of haloaryl-closo-carbaboranes. Crystal structures of 1-(4-BrC6F4)-2-R-1,2-closo-C2B 10H10 (R=Me, Ph, But)

Article abstract of DOI:10.1016/S0277-5387(99)00071-6

Reaction of C₆F₅Br with Li[1-R-1,2-closo-C₂B₁₀H₁₀] readily gives compounds 1-(4-BrC₆F₄)-2-R-1,2-closo-C₂B ₁₀H₁₀ [R=Me (1), Ph (2), Bu^t (3)]. Compounds 1-3 were characterised by NMR spectroscopy and single crystal X-ray diffraction studies. A significant lengthening of the C_cage-C_cage connectivity is seen as the steric demands of the cage bound substituents increase, from 1.712(7) A in 1 to 1.736(7) and 1.743(8) A in 2 and to 1.761(6) A in 3, the last being the longest C_cage-C_cage distance recorded for a carbaborane with alkyl or aryl substituents. Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(99)00071-6

Polyhedron 18 (1999) 1961–1968
Haloaryl carbaboranesq
2. Synthesis and characterisation of haloaryl-closo-carbaboranes. Crystal
structures of 1-(4-BrC6F4)-2-R-1,2-closo-C2B10H10 (R5Me, Ph, But)
*
Rhodri Ll. Thomas , Alan J. Welch
Department of Chemistry, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK
Received 1 December 1998; accepted 19 January 1999
Abstract
Reaction of C6F5Br with Li[1-R-1,2-closo-C2B10H10] readily gives compounds 1-(4-BrC6F4)-2-R-1,2-closo-C2B10H10 [R5Me (1), Ph
(2), But (3)]. Compounds 1-3 were characterised by NMR spectroscopy and single crystal X-ray diffraction studies. A significant
˚
lengthening of the Ccage –Ccage connectivity is seen as the steric demands of the cage bound substituents increase, from 1.712(7) A in 1 to
˚
˚
1.736(7) and 1.743(8) A in 2 and to 1.761(6) A in 3, the last being the longest Ccage –Ccage distance recorded for a carbaborane with alkyl
or aryl substituents.
1999 Elsevier Science Ltd. All rights reserved.
1. Introduction
led to the isolation of the unexpected products 1,4-(29-R-
C2B10H10)C6F4 even in the presence of excess C6F6, and
1
We are currently interested in the effects of substituted
aryl substituents on the properties of carbaboranes. Recent
work has investigated the compounds, 1-R-12-R9-1,2-
closo-C2B10H10 (R5H, Ph; R95Ph, p-Tol, p-C6H4NO2)
as potential non-linear optical (NLO) materials [1], and the
use of electron-withdrawing and -donating aryl groups is
expected to enhance such NLO properties. We are inter-
ested in polyfluorinated aryl rings as electron-withdrawing
substituents to carbaboranes. The interdependence of elec-
tronic factors and structure for clusters is codified in
Wade’s rules [2] and, so, any significant electron with-
drawal may have consequences for the structure of the
cluster. Structural deformations in the cluster may also be
induced as a result of the steric interactions of the
exopolyhedral substituents.
no mono-cage products were identified. In the present
contribution we report the synthesis and characterisation of
several haloarylcarbaboranes of general formula 1-(4-
C6F4Br)-2-R-1,2-closo-C2B10H10 where R5Me, Ph, But.
This group of compounds is considered in relation to the
analogous compounds 1-Ph-2-R-1,2-closo-C2B10H10 (R5
H [4], Br [5], Me [6], Ph [7]) in which the electron-
withdrawing fluorine atoms are absent.
2. Experimental
2.1. General
All reactions were carried out under an atmosphere of
dry, oxygen-free N2 using standard Schlenk line tech-
niques, with some subsequent manipulation in air. Solvents
were dried and distilled under nitrogen immediately prior
to use. Preparative thin-layer chromatography (TLC) em-
ployed Kieselgel 60 F254 plates (Merck), pre-washed in the
Previous attempts to synthesise haloarylcarbaboranes,
specifically pentafluorophenylcarbaboranes, by Zakharkin
and Lebedev [3], involved the reaction of Li[1-R-1,2-
closo-C2B10H10] (R5Me, Ph) with C6F6. These reactions
qFor Part 1, see Ref. [14].
*Corresponding author. Present address: Department of Chemistry,
University of Durham, South Road, Durham, DH1 3LE, UK. Tel.:
144-191-374-4642; fax: 144-191-386-1127.
1In all molecules, the haloaryl ring is attached to C(1), which involves a
renumbering of the cluster from the starting material, where C(1) bears
substituent R.
E-mail address: rhodri.thomas@durham.ac.uk (Rh.Ll. Thomas)
0277-5387/99/$ – see front matter
PII: S0277-5387(99)00071-6
1999 Elsevier Science Ltd. All rights reserved.

1962
Rh.Ll. Thomas, A.J. Welch / Polyhedron 18 (1999) 1961–1968
Table 1
Crystallographic data and details of data collection and structure refinement for compounds 1–3
1
2
3
Formula
Crystal size/mm
System
C9 H13B10BrF4
0.6030.2530.25
Monoclinic
P21 /n
6.840(3)
14.927(3)
15.902(4)
90
92.64(3)
90
1621.9(9)
4
C14H15B10BrF4
0.5030.3030.20
Triclinic
C12H19B10BrF4
0.5030.3530.30
Monoclinic
P21 /c
8.955(3)
14.930(4)
14.341(4)
90
95.11(3)
90
1909.7(10)
4
Space group
Pbar1
˚
a/A
10.901(3)
13.263(2)
13.823(3)
97.83(9)
97.12(11)
91.76(7)
1962.3(7)
4 (2 independent)
1.514
9,u,11
1.50,u,24.97
212→112
215→115
0 →16
˚
b/A
˚
c/A
a/8
b/8
g/8
3
˚
V/A
Z
Dcalc /g cm23
uorientation /8
udata collection /8
h range
1.578
1.486
8,u,11
1.87,u,24.97
28→18
0 →117
0 →118
2937
2834
1479
0.1026
9,u,11
1.97,u,24.97
210→110
0→117
0→117
3584
3357
1870
0.1033
k range
l range
Data measured
Unique data
Data observed [F,2s(F)]
g1
7291
6890
3466
0.1476
R (all data)
R (observed data)
wR(F2)
0.1531
0.0643
0.1708
0.1695
0.0828
0.2255
0.1384
0.0643
0.1770
S
0.932
0.988
1.003
Variables
Max. residue/eA
Min. residue/eA
251
0.316
20.779
561
285
0.348
20.870
23
˚
˚
0.938 (near Br)
21.639 (near Br)
23
appropriate solvent. Infra-red spectra were recorded as
solutions in CH2Cl2, referenced against the same solvent
or as KBr discs, on a Perkin-Elmer 598 or a Nicolet Impact
400 spectrophotometer. NMR spectra were recorded at
room temperature on Bruker WP200 (11B, 1H) and WH360
(1H, 19F) spectrometers. Chemical shifts are reported
relative to external SiMe4 (1H), CCl3F (19F) and BF3?
OEt2 (11B), with positive shifts to high frequency. Mi-
croanalyses were performed by the Edinburgh University
Chemistry Department. The starting materials 1-Me-
C2B10H11 [8], 1-Ph-C2B10H11 [4] and 1-But-C2B10H11 [9]
were prepared by literature methods, and their purities
the extract under reduced pressure. Recrystallisation from
MeOH gave the product as a white solid, which was dried
in vacuo. Yield51.36 g, 81%.
Found: C, 28.63%; H, 3.91%. Calculated (for
C9H13B10BrF4): C, 28.14%; H, 3.40%. IR (CH2Cl2): nmax
2550 cm21 (B–H). NMR (CDCl3): 11B-h1Hj d 0.91 (1B),
24.74 (2B) and 28.38 (7B) ppm; 19F d 2128.6 (br. s, 2F,
1
o-F) and 2130.5 (m, 2F, m-F) ppm; H: d 1.87 (s, 3H,
CH3) ppm.
2.2.1.2. Synthesis
C2B10H10 (2)
of
1-(4-BrC6F4 )-2-Ph-1,2-closo-
1
confirmed by microanalysis and H NMR spectroscopy.
To 1-Ph-1,2-closo-C2B10H11 (2.20 g, 10.0 mmol) in
diethyl ether (30 ml) at 08C was added a BuLi solution
(1.6 M, 6.8 ml, 11.0 mmol). A solution of C6F5Br (2.51 g,
11.0 mmol) in diethyl ether (5 ml) was then added to the
stirring mixture. This was then warmed to room tempera-
ture and stirred for 20 h, giving a pale orange solution. The
solvents were removed under reduced pressure to leave an
orange oil, which was extracted with hexane (3340 ml).
The solvent was removed from the extract under reduced
pressure to yield a pale, oily solid. Recrystallisation from
warm MeOH gave a white solid, 2, which was dried in
vacuo. Yield53.8 g, 85%.
2.2. Syntheses
2.2.1.1. 1-(4-BrC6F4 )-2-Me-1,2-closo-C2B10H10 (1)
To a solution of 1-Me-1,2-closo-C2B10H11 (0.704 g,
4.45 mmol) in diethyl ether (25 ml) at 08C was added a
1.6-M solution of BuLi in hexane (3.1 ml, 5 mmol). A
solution of C6F5Br (1.1 g, 4.46 mmol) in a small amount
of diethyl ether was then added. The mixture was stirred
for 30 min at room temperature, until the solution turned
dark orange. The solvents were removed under reduced
pressure to leave a brown oily solid. This was extracted
with hexane (3310 ml) and the solvent was removed from
Found: C, 38.16%; H, 4.01%. Calculated (for

Rh.Ll. Thomas, A.J. Welch / Polyhedron 18 (1999) 1961–1968
1963
C14H15B10BrF4): C, 37.60%; H, 3.38%. IR (CH2Cl2): nmax
2545 cm21 (B–H). NMR (CDCl3): 11B-h1Hj d 1.84 (1B),
22.40 (1B) and 28.23 (8B) ppm; 19F d 2129.7 (br. s, 2F,
o-F) and 2131.2 (m, 2F, m-F) ppm; H d 7.57 (d, 2H),
7.32 (m, 1H) and 7.25 (m, 2H) ppm.
Found: C, 34.64%; H, 6.04%. Calculated (for
C12H19B10BrF4): C, 33.93%; H, 5.48%. IR (CH2Cl2): nmax
2575 cm21 (B–H). NMR (CDCl3): 11B-h1Hj d 1.00 (1B),
22.69 (2B), 27.86 (3B) and 29.24 (4B) ppm; 19F: d
1
1
2129.7 (br. s, 2F, o-F) and 2131.2 (m, 2F, m-F) ppm; H:
d 1.22 (s, 9H, But) ppm.
2.2.1.3. Synthesis
C2B10H10 (3)
of
1-(4-BrC6F4 )-2-But-1,2-closo-
2.2.2. Crystallography
A diethyl ether (40 ml) solution of 1-But-1,2-closo-
C2B10H11 (0.51 g, 2.5 mmol) was treated with a solution
of BuLi in hexane (1.8 ml, 2.9 mmol). C6F5Br (0.37 ml,
2.4 mmol) in a small amount of diethyl ether was then
added. The mixture was stirred for 4 h at room tempera-
ture, until the solution turned orange, and then the solvents
were removed under reduced pressure to leave a dark, oily
solid. This was extracted with hexane (2315 ml) and the
solvent was removed from the extract under reduced
pressure. Recrystallisation from warm MeOH gave the
product, 3, as a white solid, which was dried in vacuo.
Yield50.49 g, 49%.
All data were collected on an Enraf-Nonius CAD4
diffractometer at room temperature using graphite mono-
chromated Mo–Ka X-radiation, l50.71069 A. Diffrac-
˚
tion-quality crystals of the compounds were grown by slow
evaporation of a methanol solution (compound 1) or by
diffusion between water and a methanol solution (com-
pounds 2 and 3), and were mounted in subsequently sealed
Lindemann tubes.
In Table 1 are listed crystal data, as well as details of
data collection and structure refinement, for crystals of
compounds 1, 2 and 3. For each crystal, the unit cell
parameters and orientation matrix for data collection were
determined by the least-squares refinement of the setting
angles of 25 strong, high-angle reflections. Data collection
Table 2
˚
Selected interatomic distances (A) and interbond angles (8) for compound
1
C(11)–C(1)
C(1)–B(5)
C(1)–C(2)
C(1)–B(3)
C(2)–B(7)
C(2)–B(6)
B(3)–B(7)
B(4)–B(8)
B(4)–B(9)
B(5)–B(10)
B(6)–B(10)
B(7)–B(11)
B(7)–B(8)
B(8)–B(12)
B(9)–B(12)
B(10)–B(12)
1.515(7)
1.695(8)
1.712(7)
1.743(9)
1.685(9)
1.707(9)
1.735(10) B(3)–B(4)
1.749(11) B(4)–B(5)
1.770(11) B(5)–B(9)
1.769(10) B(5)–B(6)
1.741(10) B(6)–B(11)
1.739(11) B(7)–B(12)
1.759(11) B(8)–B(9)
1.784(11) B(9)–B(10)
1.765(10) B(10)–B(11)
1.760(12) B(11)–B(12)
C(21)–C(2)
C(1)–B(4)
C(1)–B(6)
C(2)–B(11)
C(2)–B(3)
B(3)–B(8)
1.515(7)
1.706(9)
1.728(9)
1.681(9)
1.702(10)
1.734(11)
1.763(11)
1.770(11)
1.749(11)
1.772(11)
1.745(10)
1.747(10)
1.777(13)
1.749(12)
1.754(10)
1.758(11)
C(16)–C(11)–C(1) 121.6(5)
C(12)–C(11)–C(1) 125.4(5)
C(11)–C(1)–B(5)
B(5)–C(1)–B(4)
C(11)–C(1)–B(6)
C(2)–C(1)–B(6)
B(4)–C(1)–B(3)
120.8(4)
62.7(4)
118.3(5)
59.5(4)
61.5(4)
C(11)–C(1)–B(4)
C(11)–C(1)–C(2)
B(5)–C(1)–B(6)
C(11)–C(1)–B(3)
C(2)–C(1)–B(3)
C(21)–C(2)–B(7)
C(21)–C(2)–B(3)
C(21)–C(2)–B(6)
C(21)–C(2)–C(1)
B(6)–C(2)–C(1)
B(8)–B(3)–B(7)
B(8)–B(3)–B(4)
C(2)–B(6)–C(1)
B(10)–B(6)–B(11)
B(10)–B(6)–B(5)
121.8(5)
120.4(4)
62.4(4)
120.1(5)
59.0(4)
122.4(5)
117.4(6)
117.6(6)
117.2(4)
60.7(3)
60.9(4)
60.0(5)
59.8(3)
60.4(4)
60.5(4)
C(21)–C(2)–B(11) 122.1(5)
B(11)–C(2)–B(7)
B(7)–C(2)–B(3)
B(11)–C(2)–B(6)
B(3)–C(2)–C(1)
C(2)–B(3)–B(7)
C(2)–B(3)–C(1)
C(1)–B(3)–B(4)
C(2)–B(6)–B(11)
C(1)–B(6)–B(5)
62.2(4)
61.6(4)
62.0(4)
61.4(4)
58.7(4)
59.6(3)
58.2(4)
58.3(4)
57.9(4)
Fig. 1. Perspective view of a single molecule of compound 1 (30%
thermal ellipsoids except for hydrogen atoms, which have an artificial
˚
radius of 0.1 A for clarity). The aryl ring is numbered cyclically
[C(11)–C(16)], and hydrogen atoms carry the same number as the atom
to which they are attached.

1964
Rh.Ll. Thomas, A.J. Welch / Polyhedron 18 (1999) 1961–1968
was by v22u scans in 96 steps with an v scan width
(0.810.34 tan u ). Data were corrected for Lorentz and
polarisation effects, and for decay (determined by remea-
surement of the intensities of two chosen reflections every
8 X-ray h) using CADABS [10]. Only data for which
F.2.0s(F) were retained for structure solution and refine-
ment.
3. Results and discussion
In 1970, Zakharkin and Lebedev [3] attempted to
synthesise (polyfluorophenyl)carbaboranes by reaction of
Li[1-R-1,2-closo-C2B10H10] (R5Me, Ph) with C6F6, lead-
ing to the isolation of the unexpected product 1,4-(29-R-
C2B10H10)C6F4 [4] and we have recently structurally
characterised the compound where R5Ph (4) [13]. In an
attempt to produce a mono-cage product, C6F5Br was used
in place of C6F6 for reaction with Li[RC2B10H10]. Re-
crystallisation from hot methanol gave analytically pure
white crystalline products, 1-ArF-2-R-C2B10H10 (R5Me
[1], Ph [2], But [3]; ArF54-C6F4Br) in good yields.
The identities of the products were confirmed by micro-
analysis, infra-red spectroscopy and by NMR studies. The
11B-h1Hj spectra obtained showed typical features for closo
carbaboranes, with multiple peak coincidences in the
spectrum due to the small range of 11B resonances (12 to
210 ppm) found. 1H NMR spectroscopy showed that the
weakly acidic cage CH atoms have been displaced, but the
cage-bound substituents remain. 19F NMR spectra con-
tained only two resonances, for the ortho- and meta-
fluorine environments, showing that the para-position was
not occupied by a fluorine atom. It was noted in each case
that one resonance showed significant fine structure, whilst
Each structure was solved by direct methods with all
remaining non-hydrogen atoms found by difference
Fourier methods and refined on F using full matrix least-
squares (SHELXTL [11]). In compound 2, the phenyl ring
˚
was constrained to be a regular hexagon (C–C, 1.395 A).
Hydrogen atoms were placed in idealised positions, riding
on the atoms to which they were bonded. After isotropic
convergence, data were corrected for absorption effects
using empirical methods [12]. Non-hydrogen atoms were
allowed anisotropic thermal parameters. In compounds 1
and 2, the hydrogen atoms in each crystallographically
independent molecule were given a common variable
thermal parameter (UH). In compound 3, the hydrogen
atoms were given isotropic thermal parameters set at
1.2Ueq for the atom to which they were bonded (1.5Ueq for
CH3). In the final stages of refinement, data were weighted
such that w215[s2(Fo2)1(g1P)21(g2P)] where P5[max
(F2o or 0)12F2c]/3.
Fig. 2. Perspective views of each crystallographically independent molecule of compound 2 (30% thermal ellipsoids except for hydrogen atoms, which
˚
have an artificial radius of 0.1 A for clarity). The aryl rings are numbered cyclically [C(11A)–C(16A), C(11B)–C(16B) for ArF and C(21A)–C(26A),
C(21B)–C(26B) for Ph], and hydrogen and fluorine atoms carry the same number as the atom to which they are attached.

Rh.Ll. Thomas, A.J. Welch / Polyhedron 18 (1999) 1961–1968
1965
Table 3
Selected interatomic distances (A) and interbond angles (8) for compound 2
˚
C(11A)–C(1A)
C(21A)–C(2A)
C(1A)–B(6A)
C(1A)–B(4A)
C(1A)–C(2A)
C(1A)–B(5A)
C(1A)–B(3A)
C(2A)–B(6A)
C(2A)–B(7A)
C(2A)–B(11A)
C(2A)–B(3A)
B(3A)–B(8A)
B(3A)–B(7A)
B(3A)–B(4A)
B(4A)–B(9A)
B(4A)–B(8A)
B(4A)–B(5A)
B(5A)–B(9A)
B(5A)–B(10A)
B(5A)–B(6A)
B(6A)–B(10A)
B(6A)–B(11A)
B(7A)–B(11A)
B(7A)–B(8A)
B(7A)–B(12A)
B(8A)–B(9A)
B(8A)–B(12A)
B(9A)–B(12A)
B(9A)–B(10A)
B(10A)–B(12A)
B(10A)–B(11A)
B(11A)–B(12A)
1.494(9)
1.507(7)
1.745(10)
1.717(10)
1.743(7)
1.705(9)
1.746(9)
1.722(10)
1.701(10)
1.671(10)
1.735(9)
1.740(12)
1.755(10)
1.782(10)
1.744(12)
1.743(12)
1.788(11)
1.783(13)
1.775(12)
1.761(11)
1.734(11)
1.737(11)
1.746(11)
1.753(11)
1.758(11)
1.729(13)
1.776(13)
1.755(13)
1.790(13)
1.771(12)
1.761(11)
1.753(12)
C(11B)–C(1B)
C(21B)–C(2B)
C(1B)–B(6B)
C(1B)–B(4B)
C(1B)–C(2B)
C(1B)–B(5B)
C(1B)–B(3B)
C(2B)–B(6B)
C(2B)–B(7B)
C(2B)–B(11B)
C(2B)–B(3B)
B(3B)–B(8B)
B(3B)–B(7B)
B(3B)–B(4B)
B(4B)–B(9B)
B(4B)–B(8B)
B(4B)–B(5B)
B(5B)–B(9B)
B(5B)–B(10B)
B(5B)–B(6B)
B(6B)–B(11B)
B(6B)–B(10B)
B(7B)–B(11B)
B(7B)–B(8B)
B(7B)–B(12B)
B(8B)–B(9B)
B(8B)–B(12B)
B(9B)–B(12B)
B(9B)–B(10B)
B(10B)–B(12B)
B(10B)–B(11B)
B(11B)–B(12B)
1.469(9)
1.496(7)
1.725(10)
1.736(11)
1.736(8)
1.740(11)
1.775(10)
1.709(10)
1.711(10)
1.715(12)
1.738(10)
1.748(13)
1.756(12)
1.787(11)
1.74(2)
1.76(2)
1.793(13)
1.75(2)
1.76(2)
1.787(12)
1.758(12)
1.778(14)
1.778(13)
1.782(13)
1.821(14)
1.75(2)
1.78(2)
1.73(2)
1.75(2)
1.73(2)
1.76(2)
1.771(14)
C(12A)–C(11A)–C(1A)
C(16A)–C(11A)–C(1A)
C(26A)–C(21A)–C(2A)
C(22A)–C(21A)–C(2A)
C(11A)–C(1A)–C(2A)
C(11A)–C(1A)–B(3A)
C(11A)–C(1A)–B(4A)
C(11A)–C(1A)–B(5A)
C(11A)–C(1A)–B(6A)
C(2A)–C(1A)–B(3A)
B(4A)–C(1A)–B(3A)
B(5A)–C(1A)–B(4A)
B(5A)–C(1A)–B(6A)
B(6A)–C(1A)–C(2A)
C(21A)–C(2A)–C(1A)
C(21A)–C(2A)–B(3A)
C(21A)–C(2A)–B(6A)
C(21A)–C(2A)–B(7A)
C(21A)–C(2A)–B(11A)
B(11A)–C(2A)–B(6A)
B(11A)–C(2A)–B(7A)
B(6A)–C(2A)–C(1A)
B(7A)–C(2A)–B(3A)
B(3A)–C(2A)–C(1A)
C(2A)–B(3A)–C(1A)
C(2A)–B(3A)–B(7A)
B(8A)–B(3A)–B(7A)
B(8A)–B(3A)–B(4A)
C(1A)–B(3A)–B(4A)
C(2A)–B(6A)–C(1A)
C(2A)–B(6A)–B(11A)
B(10A)–B(6A)–B(11A)
B(10A)–B(6A)–B(5A)
C(1A)–B(6A)–B(5A)
124.6(7)
C(12B)–C(11B)–C(1B)
C(16B)–C(11B)–C(1B)
C(26B)–C(21B)–C(2B)
C(22B)–C(21B)–C(2B)
C(11B)–C(1B)–C(2B)
C(11B)–C(1B)–B(3B)
C(11B)–C(1B)–B(4B)
C(11B)–C(1B)–B(5B)
C(11B)–C(1B)–B(6B)
C(2B)–C(1B)–B(3B)
B(4B)–C(1B)–B(3B)
B(5B)–C(1B)–B(4B)
B(5B)–C(1B)–B(6B)
B(6B)–C(1B)–C(2B)
C(21B)–C(2B)–C(1B)
C(21B)–C(2B)–B(3B)
C(21B)–C(2B)–B(6B)
C(21B)–C(2B)–B(7B)
C(21B)–C(2B)–B(11B)
B(11B)–C(2B)–B(6B)
B(11B)–C(2B)–B(7B)
B(6B)–C(2B)–C(1B)
B(7B)–C(2B)–B(3B)
B(3B)–C(2B)–C(1B)
C(2B)–B(3B)–C(1B)
C(2B)–B(3B)–B(7B)
B(8B)–B(3B)–B(7B)
B(8B)–B(3B)–B(4B)
C(1B)–B(3B)–B(4B)
C(2B)–B(6B)–C(1B)
C(2B)–B(6B)–B(11B)
B(10B)–B(6B)–B(11B)
B(10B)–B(6B)–B(5B)
C(1B)–B(6B)–B(5B)
124.1(6)
122.0(6)
119.6(4)
120.4(4)
120.7(5)
120.4(5)
121.9(5)
119.9(5)
118.4(5)
59.6(3)
61.9(4)
63.0(4)
61.3(4)
59.2(4)
118.9(5)
118.0(5)
119.0(5)
121.8(5)
122.1(5)
61.6(4)
62.4(4)
60.5(4)
61.4(4)
60.3(3)
60.1(4)
58.4(4)
60.2(5)
59.3(5)
58.2(4)
60.4(4)
57.8(4)
61.0(5)
61.0(5)
58.2(4)
123.8(6)
121.1(4)
118.9(4)
119.6(5)
122.0(5)
124.3(6)
120.5(6)
116.5(5)
59.4(4)
61.2(4)
62.1(5)
62.1(5)
59.2(4)
119.2(5)
118.2(5)
119.0(5)
120.4(5)
121.7(5)
61.8(5)
62.5(5)
60.1(4)
61.2(5)
61.4(4)
59.2(4)
58.6(4)
61.1(5)
59.6(6)
58.3(4)
60.7(4)
59.3(5)
59.8(6)
59.1(6)
59.4(4)

1966
Rh.Ll. Thomas, A.J. Welch / Polyhedron 18 (1999) 1961–1968
the higher frequency resonance was a very broad singlet.
This latter resonance was assigned to the ortho fluorine
atoms by analogy with the 19F NMR spectra of 4, which
showed only one broad signal from its fluorine atoms, all
of which are ortho to a carbaborane cage. The broadening
is assumed to be due to long-range coupling to the boron
nuclei in the cluster. The products were as expected for a
SNAr reaction, with substitution para to the least elec-
tronegative substituent, which was bromine in this case.
Compounds 1–3 form a series analogous to the 1-
phenylcarbaboranes, with intersubstituent steric interac-
tions growing as we increase the size of the C(2) sub-
stituent. A large series of carbaboranes, 1-Ph-2-R-1,2-
C2B10H10 [e.g. R5H (5) [4,14], Br [5], Me (6) [6], Ph (7)
[7], Me3Si (8) [15]] has been reported and compounds 1
and 2 are directly analogous to two of these. The non-
fluorinated analogue of 3, [1-Ph-2-But-C2B10H10], how-
ever, has not been reported, although many attempts to
synthesise it have been made [9]. Since the haloaryl
carbaborane 3 forms easily, we can discount steric grounds
for this failure.
graphic study (Scheme 1). Fig. 1 views a single molecule
and demonstrates the atomic numbering scheme adopted
whilst Table 2 presents selected molecular parameters. In
this molecule, intersubstituent steric effects are expected to
be the smallest, and the Ccage –Ccage interatomic distance is
˚
1.712(7) A, which is not significantly longer than the
˚
1.696(5) A distance found in 6, although both are greater
than that found in the unsubstituted ortho-carbaborane, i.e.,
˚
1.630(6) A [16]. Intersubstituent steric interactions will
also affect the orientations adopted by the aryl rings. The
orientation of phenyl rings attached to carbaboranes has
previously been described by the parameter u, the modulus
of the average of the two Ccage –Ccage –Cring –Cring torsion
angles, and we may use this parameter to describe the
orientation of an aryl ring also. Thus, u5908 when the aryl
ring lies in the Ccage –Ccage –Cring plane, and u508 when
the ring lies perpendicular to this plane. Calculations have
suggested that the electronically preferred orientation of
the phenyl ring in 5, where intersubstituent effects are
small, is u5688 [4]. In compound 1, u56.8(9)8, which is
substantially reduced by the large intersubstituent effects
and is even lower than that found in 6 (u516.78).
The identity of compound 1 was confirmed by crystallo-
Compound 2 crystallises with two independent mole-
Fig. 3. Perspective view of a single molecule of compound 3 (30%
thermal ellipsoids except for hydrogen atoms, which have an artificial
˚
radius of 0.1 A for clarity). The aryl ring is numbered cyclically
[C(11)–C(16)], and hydrogen atoms carry the same number as the atom
to which they are attached.
Scheme 1.

Rh.Ll. Thomas, A.J. Welch / Polyhedron 18 (1999) 1961–1968
1967
Table 4
Selected interatomic distances (A) and interbond angles (8) for compound 3
˚
C(11)–C(1)
C(21)–C(211)
C(21)–C(213)
C(1)–B(3)
C(1)–B(5)
C(2)–B(3)
C(2)–B(7)
B(3)–B(4)
B(3)–B(8)
B(4)–B(8)
B(5)–B(6)
B(5)–B(10)
B(6)–B(11)
B(7)–B(11)
B(8)–B(9)
B(9)–B(10)
B(10)–B(11)
B(11)–B(12)
1.501(6)
1.497(8)
1.518(9)
1.737(8)
1.719(9)
1.731(8)
1.702(8)
1.773(11)
1.756(10)
1.756(10)
1.766(10)
1.752(9)
1.752(8)
1.740(10)
1.776(14)
1.747(13)
1.773(10)
1.768(10)
C(21)–C(212)
C(21)–C(2)
C(1)–C(2)
C(1)–B(4)
C(1)–B(6)
C(2)–B(6)
C(2)–B(11)
B(3)–B(7)
B(4)–B(5)
B(4)–B(9)
B(5)–B(9)
B(6)–B(10)
B(7)–B(8)
B(7)–B(12)
B(8)–B(12)
B(9)–B(12)
B(10)–B(12)
1.500(9)
1.569(7)
1.761(6)
1.726(8)
1.745(8)
1.742(8)
1.703(8)
1.770(9)
1.787(12)
1.754(11)
1.740(12)
1.752(10)
1.773(11)
1.755(10)
1.787(12)
1.760(11)
1.785(12)
(16)–C(11)–C(1)
C(211)–C(21)–C(212)
C(212)–C(21)–C(213)
C(212)–C(21)–C(2)
C(11)–C(1)–B(5)
B(5)–C(1)–B(4)
B(4)–C(1)–B(3)
B(5)–C(1)–B(6)
B(3)–C(1)–C(2)
C(21)–C(2)–B(7)
B(7)–C(2)–B(11)
B(7)–C(2)–B(3)
C(21)–C(2)–C(1)
B(6)–C(2)–C(1)
C(2)–B(3)–B(7)
C(1)–B(3)–B(4)
C(2)–B(6)–C(1)
C(1)–B(6)–B(5)
B(10)–B(6)–B(11)
123.4(4)
C(12)–C(11)–C(1)
C(211)–C(21)–C(213)
C(211)–C(21)–C(2)
C(213)–C(21)–C(2)
C(11)–C(1)–B(4)
C(11)–C(1)–B(3)
C(11)–C(1)–B(6)
C(11)–C(1)–C(2)
B(6)–C(1)–C(2)
C(21)–C(2)–B(11)
C(21)–C(2)–B(3)
B(11)–C(2)–B(6)
B(3)–C(2)–C(1)
C(2)–B(3)–C(1)
B(8)–B(3)–B(7)
B(8)–B(3)–B(4)
C(2)–B(6)–B(11)
B(10)–B(6)–B(5)
123.4(4)
106.9(6)
107.2(6)
112.7(5)
119.3(4)
62.5(4)
61.6(4)
61.3(4)
59.3(3)
121.3(4)
61.5(4)
62.1(3)
120.9(4)
59.7(3)
58.1(3)
58.9(4)
60.7(3)
58.6(3)
60.8(4)
106.3(7)
110.4(5)
112.9(5)
118.9(4)
120.2(4)
120.8(4)
123.3(4)
59.6(3)
121.3(4)
119.4(4)
61.1(3)
59.7(3)
61.0(3)
60.4(4)
59.7(4)
58.4(3)
59.7(4)
cules in the asymmetric unit, and both are illustrated in
Fig. 2. Selected interatomic distances and interbond angles
are given in Table 3. The intersubstituent steric effects in 2
may be minimised by the two aryl rings both adopting low
u values. Such an effect is observed in both independent
molecules, although to different extents, with the values of
uPh and uAr being smaller in molecule A [uAr52.5(7)8;
uPh52.3(10)8] than in molecule B [uAr56.8(7)8; uPh5
10.3(10)8]. Similar orientations of aryl rings are found in
the structures of 4 and 7, where the aryl rings are in similar
environments to those in molecule 2.
atoms of the ArF group to the plane of the non-fluorinated
ring.
The structure of 3 was also determined by crystallo-
graphic study, and is shown in Fig. 3, with selected
molecular parameters in Table 4. The extremely low value
of u [0.1(8)8] found is an expected consequence of the
extremely bulky C(2) substituent. Intersubstituent steric
effects are significant, and these may induce other distor-
tions in addition to the lengthening of the C(1)–C(2)
connectivity. Most noticeable is the ‘bend back’ of the aryl
The C(1)–C(2) interatomic distances found in 2 are
˚
˚
Table 5
1.743(7) A (2a) and 1.736(8) A (2b) and, although these
are numerically larger, they are not significantly different
from those in the non-halogenated analogue 7, 1.733(4)
11B chemical shifts in a series of carbaboranes, 1-Ar-2-R-C2B10H10
Ar
R
Range/ppm
Weighted mean/ppm
˚
and 1.720(4) A. These values are larger than those found
1
2
3
6
7
ArF
ArF
ArF
Ph
Me
Ph
10.91→28.38
11.70→28.40
11.00→29.24
22.36→29.36
22.07→28.60
26.72
25.21
26.49
27.77
26.97
for carbaboranes where the C(2) substituent is a methyl
group, due to increased steric interactions between the
C(2) substituent and the aryl ring. Such interactions are
tBu
Me
Ph
Ph
˚
indicated by the close approach (ca. 2.8 A) of the fluorine

1968
Rh.Ll. Thomas, A.J. Welch / Polyhedron 18 (1999) 1961–1968
ring away from the sterically demanding tertiary butyl
group, giving a C(2)–C(1)–C(11) angle of 123.3(4)8,
compared with ca. 1208 in compounds 1, 2 and 4. The
close contacts of the two substituents are also notable, with
Supplementary data
Crystallographic data have been deposited at the Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1E7, UK, and data may be obtained on
request, quoting the deposition codes CCDC 111940,
111941 and 111942.
˚
two butyl hydrogen atoms lying ca. 2.5 A from the plane
˚
of the ring. A C(1)–C(2) distance of 1.761(6) A is the
result of these effects, which is considerably longer than in
the previous haloaryl carbaboranes. Indeed, this distance is
only known to be surpassed by that in three other closo-
carbaboranes, all of which contain non-carbon atoms as
substituents to the cage; oxygen in one case [17], and
sulfur in the others [18]. The distance surpasses the length
of the most similar carbaborane, 1-Ph-2-Me3Si-1,2-closo-
Acknowledgements
We acknowledge Heriot-Watt University for a student-
ship (Rh. Ll. T.) and the Callery Chemical Company for a
generous gift of decaborane.
˚
C2B10H10, at 1.708(4) A, which is as expected due to the
smaller steric influence of the Me3Si group relative to the
Me3C group, a consequence of the longer Ccage –Si bond.
The structural effects of replacing Ph by ArF do not
appear to be significant in these molecules, suggesting
either that the replacement has little electronic effect on the
cluster or that any electronic changes do not affect the
structure. Any electronic changes in this series of haloaryl
carbaboranes may be identified by examining their 11B
chemical shifts, which are shown in Table 5, since
significant reduction in electron density should lead to a
deshielding of the 11B nuclei. Only a change of 1.05–1.75
ppm is seen in the average 11B resonances, although a
more significant shift of ca. 3.5 ppm is seen in the highest
frequency resonances. These are the integral one reso-
nances, which identifies them as arising from B(9) or
B(12), antipodal to C(2) and C(1), respectively. This large
effect of substitution on these specific boron atoms, the
so-called ‘antipodal effect’, has been well documented
[19]. The small deshielding upon replacement of Ph by ArF
does not represent a large transfer of the cluster electron
density to the aryl ring, in agreement with the observed
structures.
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–
´
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Inorg. Chem. 29 (1990) 149.
´
´
´
[19] S. Hermanek, T. Jelınek, J. Plesek, B. Stıbr, J. Fusek, F. Mares, in:
´
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